1. Field of Invention
The invention relates to an apparatus for calling a central computer and transmitting information over the telephone lines.
Definitions
For clarity and understanding the following definitions will be used:
a. Meter Interface Unit (MIU) refers to an electronic unit located at a customer's residence, and connected to the telephone line. The MIU interfaces with a meter encoder to provide meter data readings. The MIU connects to a telephone line through a switched telephone network. The MIU reports meter data readings to a central computer via the telephone line. PA1 b. Central computer refers to a computer located at a utility office. The central computer is equipped with modems and telephone lines for placing and receiving telephone calls to and from the MIU. PA1 c. Microprocessor is the command processing center of the MIU. PA1 d. Dial In-bound MIU refers to a MIU which calls a central computer via the telephone line for the purposes of data transmission. PA1 e. Dial Out-bound MIU refers to a MIU which receives a call from a central computer for the purpose of initiating a data transmission cycle. PA1 f. On-hook refers to the state of a telephone instrument when the handset is in its normal position on the body of the telephone instrument. PA1 g. Off-hook refers to the state of a telephone instrument when the telephone is in use. The off-hook state occurs when the handset is lifted from the body of the telephone instrument such that current flows to the telephone instrument. PA1 h. Ring signals are signals on the telephone line indicating that a telephone call is being placed to the customer's telephone.
2. Description of the Prior Art
Dial in-bound meter interface units (MIU) dial-up a central computer for purposes of transmitting utility meter data. The MIU dials up the central computer periodically or at a predetermined time. A typical MIU dial-up function requires the remote unit to seize the telephone line and dial the telephone number for the central computer. Once a connection is established, the MIU reports the desired information.
Power to operate an MIU is generally obtained from the installation site, i.e., the customer's premises, or from an external power supply such as a battery. Drawing power from the installation site causes the undesirable result of increasing the customer's energy consumption. Thus, resulting in higher energy costs to the customer.
U.S. Pat. Nos. 4,455,453; 4,469,917; 4,847,892; and 4,578,534 all disclose dial in-bound MIUs powered by an external battery. The use of an external battery renders the MIU more costly to maintain. External battery supplies also interfere with the installation of MIUs in confined spaces such as pits.
U.S. Pat. No. 4,847,892 discloses a MIU having both dial in-bound and remote monitoring capabilities. During the dial in-bound cycle, the MIU calls up the central computer at a preset time. Timing control functions are regulated by a clock in the MIU system. In the remote monitoring phase, a clock controlled timing circuit connects the data set to a subsystem which stands-by during a predetermined time interval to detect a call from the central computer. The operation and maintenance of the disclosed device, however, is hampered by the need for an external power supply.
U.S. Pat. No. 5,134,650 is described as disclosing a dial in-bound MIU. However, the disclosed invention actually performs as a dial out-bound MIU. Generally, in dial out-bound system, the central computer calls the remote unit to initiate data transmission.
In U.S. Pat. No. 5,134,650, the MIU monitors the telephone line for the detection of ring signals. When a ring signal is detected, the MIU determines whether the telephone was answered, i.e., whether the telephone is on or off-hook. If the telephone is on-hook, the MIU continues to monitor the line. If the telephone is off-hook, the MIU monitors the telephone line to determine when the telephone goes back to on-hook state. As soon as on-hook conditions are detected, the MIU seizes the telephone line. The MIU searches the telephone line for a modem answer tone issued by the central computer. If the modem answer tone is detected, the MIU connects the telephone line to the modem of the automatic metering equipment. This completes the connection to the central computer. Thus, the remote unit never calls the central computer. The remote simply comes on line to begin data transmission if it detects the appropriate command from the central computer.
The disclosed MIU does not contain a clock or timing mechanism. The MIU does not have the capacity to self initiate a call to the central computer. The MIU requires customer or utility company intervention before a meter read and data transmission can take place.
U.S. Pat. No. 4,644,103 discloses a meter interface unit which derives its operating current from a telephone line. Telephone line current is used to energize a tone detection circuit. The tone detection circuit is responsible for determining if the MIU is being interrogated by the central computer. The tone detection circuit is an intermittently functioning circuit. Power dissipation is required every few seconds to ensure proper functioning of the circuit. Unfortunately, the short power discharge intervals associated with this device limit its capability to signal detection only. Moreover, the telephone must be frequently placed in the off-hook state to accommodate recharging of a voltage regulating capacitor. The constant recharging of the capacitor increases the likelihood of causing interference with the customer's use of the telephone line.
The prior art does not enable a dial in-bound MIU to draw all of its operating current from the telephone line. The prior art only enables a MIU to draw sufficient current from the telephone line to detect a pulse, indicating that a data transmission is requested.
Furthermore, Utility Regulation, 47 C.F.R. .sctn. 68,312, limits the amount of current which can be drawn from telephone lines while the telephone is in the "on-hook" state. The on-hook state results when the telephone handset is in place on the telephone instrument. The handset depresses a switch which disconnects the telephone instrument from the telephone line, resulting in an open circuit. During on-hook conditions, any device connected to the telephone line must have an effective resistance between tip and ring of greater than 5 megohms. A 5 megohm resistance corresponds to about 9.6 microamps of available supply current at 48 volts.
When the handset is lifted "off-hook" the telephone is connected to the line and current flows to the telephone instrument. In the off-hook state, the telephone is available for use. When the telephone is in the off-hook state, utility regulation 47 C.F.R. 68.312 no longer limits the current which may be drawn from the telephone line.
The disadvantages associated with existing systems are many. Existing systems require an external source of power. This power is obtained either from the installation site or provided by an external battery. External power sources make the MIU more costly to install and maintain. Additionally, external power supplies interfere with the installation of the MIU in small confined areas. Further, existing MIUs are programmed to communicate with the central computer only at a pre-selected time or during a pre-selected time interval.
Therefore, a dial in-bound MIU having the capacity to derive all of its operating current from the telephone line and to make scheduled and unscheduled calls to the central computer has not been achieved in the prior art. An MIU having the aforementioned attributes overcomes the disadvantages associated with prior art MIUs.